Process of treating cellulosic material



Patented Dec. 25, 1945 PROCESS OF TREATING CELLULOSIC MATERIAL CliffordI. Haney and Mervin E. Martin, Cumberland, Md., assignors to CelaneseCorporation of America, a corporation of Delaware No Drawing.Application January 20, 1942. Serial No. 427,440

19 Claims.

This invention relates to the treatment of cellulosic materials infibrous form for the purpose of rendering them more suitable foresterification, especially acetylatlon, and also to the production ofcellulose acetates or other cellulose esters from such treatedmaterials.

An object of our invention is to treat cellulosic materials so as torender them more reactive to acetylation or other esteriflcation.

Another object of our invention is to obtain cellulose esters yieldingsolutions of improved clarity.

Still another object of our invention is the preparation of celluloseesters from said treated materials whereby the course of the reactionmay be more readily controlled and the heat generated during thereaction dissipated or removed with ease and economy.

Other objects of our invention will appear from the following detaileddescription.

While our invention will be more particularly described in connectionwith the preparation of been proposed to pretreat the cellulosicmaterials employed so as to render said materials more reactivetoesterlfying agents so that cellulose esters of improved propertiesmight be obtained. In pretreating said cellulosic materials, variousexpedients have been employed. In some instances, the cellulosicmaterials. have been given a pretreatment with alkaline swelling agentsto cause them to become more easily esterifiable and in other instancesit has been proposed to pretreat said materials with organic acids,either in liquid or vapor form. These pretreatments have been of somevalue in increasing the reactivity of the cellulosic materials sotreated, but the properties, such as clarity, of the resulting celluloseesters have not always beenwholly satis factory.

We now have discovered that cellulose esters yielding solutions ofincreased clarity, and which may be formed into yarns of improvedproperties. may be prepared from cellulosic materials by pretreatingsaid cellulosic materials, prior to esteriflcation, with a mixture oflower aliphatic acids, one of which is formic acid, and havingincorporated therein a small amount 01' a mineral I in accordance withour invention, cellulose aceta e 01' improved clarity may be preparedfrom cellulosic materials by pretreating said materials with an acidmixture containing formic acid, acetic acid and sulphuric acid, andthen, after pretreatment, acetylating said cellulosic material withacetic anhydride in accordance with the usual procedure. Due to thereactivity of the materials treated in this way, the acetylation takesplace rapidly and completely and the resulting cellulose acetatepossesses unusually desirable characteristics.

In pretreating said cellulosic materials prior to esterification,various lower aliphatic acids may be employed in combination with formicacid and sulphuric acid to produce the desired reactivity in thecellulosic materials. While we preferably employ acetic acid in saidpretreatment mixtures, particularly in pretreating prior to acetylation,other acids such as proplonic acid and butyric acid may likewise beemployed.

The quantity as well as the composition of the acid mixture used in thepretreatment may be varied within rather wide limits. It has been foundthat if glacial acetic acid is employed in the pretreatment, excellentresults may be obtained by employing 20 to 200 parts by weight of theglacial acetic acid to 100 parts by weight of cellulose. With theglacial acetic acid there may be employed from 1 up to 20 parts byweightof formic acid and from V: to 2 parts by weight of sulphuric acid.Preferably, we employ formic acid in amounts of from 1 to 10 parts byweight per 100 pads of cellulose, but the best results are obtained withfrom 1 to 5 parts by weightof formic acid per 100 parts of cellulose.Sulphuric acid is most preferably present in the pretreatment mixture inamounts of about 0.5 to 1 part per 100 parts of cellulose. While theacids employed may be anhydrous, we have found that the presence ofsmall amounts of water is not harmful. Thus, we preferably employ formicacid of strength and acetic and sulphuric acids of a strength of from 98to 100%, but more dilute acids may also, if desired, be emp yed.

The pretreatment is preferably carried out at room temperature, forexample, at from 16 to 30 C. but higher or lower temperatures may alsobe employed. Thus, the pretreatment may be carried out at temperaturesas low as 15 C. or-at temperatures as high as 50 C. The time oftreatment maybe varied from A hour to 3 hours. depending on theconcentration, amount and nature of the acid mixture employed as well asthe temperature of treatment.

In applying the pretreatment of our invention, the acid mixture isdistributed evenly over the cellulosic material as, for instance, byspraying, and the cellulosic material may be turned or tumbled from timeto time if necessary to insure uniform impregnation. The material towhich the acid mixture has been applied is then allowed to stand, forthe time indicated, until a product having the desired degree ofreactivity is obtained;

As cellulosic materials, we may employ, cotton cellulose or wood pulp,or similar fibrous cellulosic materials derived from various othersources such as, for example, bamboo, reeds, jute, esparto, straws, suchas linseed and hempseed straw, grasses, peanut hulls, barks, etc.

The esteriflcation of the pretreated cellulosic materials may, ifdesired, be carried out in the usual way, that is, by adding a mixtureof acid anhydride, an esterification catalyst and a solvent to thepretreated cellulosic materials, or entering the latter into a bathcomprising such mixture, and allowing the esterification to proceed toany desired stage. The cellulose ester thus formed is then ripened,precipitated from solution, washed, and stabilized, if desired. Thismethod of esterification, however, necessitates the use of intensiverefrigeration since the esterification reaction is an exothermic one andsubstantial quantities of heat ar generated. For reasons of temperaturecontrol not only must the mixture containing the esterification agent becooled substantially before the reaction but the reaction mass as wellmust be positively cooled during this reaction so that the resultantrise in temperature will not be sufficiently great to cause a partialdegradation of the cellulose. This use of intensiverefrigeration is notonly costly but frequently it is difllcult, in large scaleesterification, to obtain satisfactory temperature control even with theuse of refrigeration.

This difllculty may be overcome, however, and the esterlfication of thecellulosic materials carried out under precise temperature control ifthe fibrous cellulosic materials, activated as heretofore described, areesterified in a plurality of stages by the progressive addition of theacid anhydride to the pretreated cellulosic materials. Thus, partialesterification may be caused to take place in the pretreatment chamberby the addition of a portion of the acid anhydride needed foresterification to the activated cellulosic material in the presence ofthe sulphuric acid employed in the acid pretreatment mixture. The smallamount of sulphuric acid present enables a partial esterification of thecellulosic material to take place without generation of a large amountof heat. The partially esterifled cellulosic material, which stillretains its original fibrous form, may then be treated with the majorportion of the esterification catalyst and the acid anhy-,

dride, and the esterification reaction then allowed to proceed to thedesired degree. Since a substantial amount of the total heat of reactionis dissipated inithe first stage of the acetylation or otheresterification in the pretreater,

the amount of heat of reaction generated in the;

main esterification stage is not so great and can be dissipated withrelatively little difllculty. Since only a limited amount of catalyst ispresent when the initial addition of acid anhydride takes place in thepretreater, the resulting esterification reaction does not-proceed withundue rapidity and this, of course, serves to limit the amount of heatevolved per. unit time. The refrigeration system does not have to copewith the sudden generation of large quantities of heat, as is the casewhere all the anhydride is added in one step in the presence of the fullamount of catalyst. Since no sudden large rise in temperature occurs,the temperature and course of the main esteriflcation reaction arealways under precise control and, as a result, cellulose esters ofimproved characteristics can be obtained.

In the preparation of cellulose acetate, for example, by progressiveesterification in accordance with our process, the cellulose materialsto be acetylated preferably are first subjected to a pretreatment, asdescribed, with a mixture of acetic acid, formic acid and sulphuricacid. After pretreatment, and without the removal of the pretreatingacids, the activated cellulosic materials are then progressivelyacetylated by the addition of acetic anhydride thereto. In carrying outour novel acetylation process, as stated, only a limited portion of thetotal quantity of anhydride which is necessary to attain the desiredfinal degree of acetylation is added in the pretreater or pretreatmentchamber. The proportion of the anhydride which may be added for theinitial esterification may be varied. Thus, for example, desirableresults may be obtained when from 10 to 50% of the total quantity ofacetic anhydride necessary for acetylation is added in the pretreater,but, preferably, we add from 30 to 50%. In general, this corresponds tofrom 'l'lto 130% based on the weight of the cellulosic materials beingacetylated. The acetic anhydride, either alone or mixed with a diluentsuch as acetic acid, may be applied to the pretreated fibrous cellulosicmaterial by spraying, sprinkling Or in any other manner. The cellulosicmaterial may be tumbled or mixed during such application in order toinsure a uniform distribution of the anhydrid liquid. The anhydride maybe sprayed or sprinkled onto the pretreated cellulosic materialcontinuously until the desired amount has been added or it may besprinkled or sprayed in several increments at short intervals. When adiluent such as acetic acid is used, it may be present in amounts up tobased on the anhydride,

Both th pretreated cellulosic materials and the acetic anhydride for theinitial acetylation are preferably cooled prior to .the addition of theanhydride to the pretreater containing the cellulosic materials.Usually, satisfactory control of the temperature may be obtained whenthe pretreated cellulosic material is cooled in the pretreater to from20 to 35 C. before the addition of the anhydride, and the anhydridesolution cooled to from (minus) 10 to +15 C. before being added. Thecooling of the pretreated cellulosic materials in the pretreatmentchamber may be accomplished by circulating water, cooled to about 10 C.through a cooling jacket surrounding the chamber. Cooling the cellulosicmaterials to below about 20' C, is usually unnecessary since adequatetemperature control may usually be achieved even with such moderatecooling. The temperatur of the reacting cellulose and anhydride ispreferably maintained at from 20 u to 40 c. during the first stage ofthe acetylation in the pretreater, which reactionmay usually becompleted in from 30 to 60 minutes. The 'degree of acetylation in thepretreater may vary but is usually carried to the point where thecellulose material has an scetyl value of from 17 up to 35% (calculatedas acetic acid). Preferably, the acetyl value is 26 to 30%.

The final acetylation of the partially acetylated fibrous cellulosicmaterial may then be carried out by charging the latter into a suitableacetylizer containing an acetic acid solution of the remaining aceticanhydride to be added, together with the. desired amount ofesterification catalyst, usually sulphuric acid. Other esterificationcatalysts such as perchloric acid or sulfoacetic acid may also beemployed in the final acetylation. The mixture in the acetylizer ispreferably cooled before the fibrous, partially acetylated cellulosicmaterial is entered and the temperature to which it is cooled prior tocharging may be from to +5 C. By cooling the esterification mixtureprior to charging, the rise in temperature during the course ofesterification reaction is suiiiciently counteracted so that thetemperature rise is held to a minimum and further cooling of theacetylizer may be dispensed with. I

The esteriflcation may be so carried out that the resulting celluloseester is obtained in solution, or, if desired, the cellulose ester maybe obtained in suspension by carrying out the esterification in thepresence of a relatively large proportion of a suitable diluent in whichthe cellulose ester is insoluble. In the case of cellulose acetate,diluents such as toluene, benzene or other aromatic hydrocarbons aresuitable.

In order further to illustrate our invention, but without being limitedthereto, the following examples are given:

Example I 700 parts by weight of cotton linters contained in a suitablechamber are pretreated by spraying said linters with an acid mixturecontaining 3.5 parts by weight of 98% sulphuric acid, 175 parts byweight of 99.8% acetic acid and 70 parts by weight of 85% formic acid.The linters are tumbled during the spraying operation to ensure uniformdistribution and action of the liquid and the linters are then allowedto stand for 3 hours at a temperature of 22 C. The pretreatment causesthe resulting linters to be highly reactive and they may then beesterifled, if desired, in the yzsyual manner to yield a product ofunusual clar- More advantageously, however, the pretreated cellulosicmaterials are acetylated by the progressive addition of acetic anhydrideas follows. The 700 parts of pretreated cotton linters containing thepretreating liquid are cooled by circulating water at a temperature C.through the cooling jacket of the pretreater. After the treated lintersare cooled, a mixture of 700 parts by weight of 97% acetic anhydride and455 parts by weight of 99.8% acetic acid is cooled to 10 C. and sprayedonto the linters in three approximately equal parts over a period ofabout 8 hours. During the addition of the cooled anhydride solution, thetemperature rises to a maximum of 22 C. and after the anhydride has beencompletely added the temperature drops to 18 C. While the addition ofeach portion of the anhydride solution causes a further reaction withthe cellulosic materials and hence some evolution of heat due to theexothermic character of the reaction, the fact that the anhydridesolution is cooled prior to being added and that the degree ofesterification is limited to a partial acetylation serves to conatedcotton linters have an acetyl value of 28%, calculated as acetic acid.

After the addition of this portion of the acetic anhydride solution iscompleted, and the temperature remains constant, the partiallyacetylated cotton linters are ready for the final acetylation in anacetylizer. Before charging, there is added to the acetylizer 1,600parts by weight of 99.8% acetic acid, 1,295 parts by weight of 97%acetic anhydride and 66.5 parts of 98% sulphuric acid, which mixture iscooled to 0.5 C. The partially acetylated cotton linters are thencharged into the acetylizer and the acetylation reaction then proceedswith the reaction temperature reaching a peak of 37 C. after 1% hourswith no additional cooling being necessary.

The resulting solution contains the primary cellulose acetate which maythen be ripened as desired to any degree of solubility, e. g. acetonesolubility, after which the cellulose acetate may then be precipitated,washed and dried. When spun from an acetone solution, this celluloseacetate gives yarns of superior tenacity.

Example II 700 parts by weight of cotton linters in a suitable chamberare pretreated by spraying said linters with an acid mixture containing3.5 parts by weight of 98% sulphuric acid, 7 parts by weight of 85%formic acid and 245 parts by weight of 99.8% acetic acid. The acidmixture is uniformly distributed by tumbling the linters during thespraying and after all the acid mixture is added, the linters areallowed to stand for 8 hours at 25 C. The pretreated linters may then beacetylated, if desired, in the usual manner,.but preferably theacetylation is carried out progressively as follows:

The cotton linters, pretreated as above, are cooled to 19 C. and arethen sprayed continuously with 735 parts by weight of acetic anhydridecooled to 3 C. No acetic acid is added with the anhydride. Thetemperature drops upon addition of the anhydride and then risesgradually to a maximum of 33.5 C. which is reached 35 minutes after allthe acetic anhydride has been added, at whichpoint the temperaturebegins to drop. The resulting acetylated cellulose has an acetyl valueof 17.7% (calculated as acetic acid). An acetylizer is then charged witha mixture of 1,085 parts by weight of 97% acetic anhydride, 2,185 partsby weight of 99.8% acetic acid and 94.5 parts by weight of 98% sulphuricacid, the mixture being cooled to 0 C. The cotton linters,

pretreated as above, are then charged into the acetylizer. After theacetylation has proceeded for 1% hours, an additional 100 parts-byweight of acetic anhydride are added to the reaction mixture to ensurecomplete acetylation of all the linters present. The temperature risesto a peak of 41 C. in about 1 hour and the acetylation is completed.about 2 hours after charging. The acetic acid solution of celluloseacetate is then ripened to acetone solubility, precipitated,

trol the temperature of the reaction, thus prewashed and dried. Theresulting cellulose acetate is of very high clarity.

It is to be understood that'the foregoing detailed description is merelygiven by way of illus tration and that many variations may be madetherein without departing from the spirit of our invention.

Haying described our invention, what we desire to secure by-LettersPatent is:

1. In a process for the manufacture of a lower fatty acid ester ofcellulose ,with the aid of a lower fatty acid anhydride, the step whichcomprises pretreating a cellulosic material-in fibrous form with amedium comprising a mixture of lower aliphatic acids, one of which isformic acid, and having incorporated therein a small amount of a mineralacid esterification catalyst, the formic acid being present in an amountof from 1 to 20% by weight of the cellulose.

2. In a process for the manufacture of a lower fatty acid ester ofcellulose with the aid of alower fatty acid anhydride, the step whichcomprises pretreating a cellulosic material in fibrous form with amedium comprising a mixture of lower aliphatic acids, one of which isformic acid, and having incorporated therein a small amount of sulfuricacid, the formic acid being present in an amount of from 1 to 20% byweight of the cellulose.

3. In a process for the manufacture of cellulose acetate with the aid ofacetic anhydride, the step which comprises pretreating a cellulosicmaterial in fibrous form with a medium comprising a mixture of formicacid and acetic acid, said mixture having incorporated therein a smallamount of a mineral acid esterification catalyst, the formic acid beingpresent in an amount of from 1 to 20% by weight of the cellulose.

4. In a process for the manufacture of cellulose acetate with the aid ofacetic anhydride, the step which comprises pretreating a cellulosicmaterial in fibrous form with a medium comprising a mixture of formicacid and acetic acid, said mixture having incorporated therein a smallamount of sulfuric acid, the formic acid being present in an amount offrom 1 to 20% by weight of the cellulose.

5. In a process for the manufacture of cellulose acetate with the aid ofacetic anhydride, the step which comprises pretreating a cellulosicmaterial in fibrous form with a medium comprising a mixture of loweraliphatic acids, said mixture containing, on the weight of thecellulosic material, from 1 to 20% of formic acid, from 20 to 200% ofacetic acid and from /2 to 2% of sulfuric acid.

6. In a process for the manufacture of cellulose acetate with the aid ofacetic anhydride, the steps which comprise pretreating a cellulosicmaterial in fibrous form with a medium comprising a mixture of loweraliphatic acids, said mixture containing, on the weight of thecellulosic material, from 1 to 20% offorr'nic acid, from 20 to 200% ofacetic acid and from /3 to 2% of sulfuric acid, and maintaining saidpretreated cellulosic material at a temperature of from 16 to 50 C. for30 to 180 minutes before effecting the acetylation of said cellulosicmaterial.

7. In a process for the manufacture of a lower fatty acid ester ofcellulose with the aid of a lower fatty acid anhydride, the steps ofpretreating a cellulosic material in fibrous form with a mediumcomprising a mixture of lower aliphatic acids, one of which is formicacid, and having incorporated therein a small amount of a mineral acidesterification catalyst, the formic acid 1 being present in an amount offrom 1 to 20% by weight of the cellulose, mixing the pretreatedcellulosic material with an organic acid anhydride under such conditionsthat the cellulosic material is partially esterified while retaining itsfibrous form, and then continuing the esterification by mixing saidpartially esterified fibrous cellulosic material with an esterificationmixture comprising said organic acid anhydride and esteriflcationcatalyst.

8. In a process for the manufacture of a lower fatty acid ester ofcellulose with the aid of a lower fatty acid anhydride, the steps ofpretreating a cellulosic material in fibrous form with a mediumcomprising a mixture of lower aliphatic acids, one of which is formicacid, and having inc'orporated therein a small amount of sulfuric acid,the formic acid being present in an amount of from 1 to 20% by weight ofthe cellulose, mixing the pretreated cellulosic material with an organicacid anhydride under such conditions that said cellulosic material ispartially esterified while retaining its fibrous form, and thencontinuing the esterification by mixing said partially esterifiedfibrous cellulosic material with an esterification mixture comprisingsaid organic acid an hydride and sulfuric acid.

9. In a process for the manufacture of cellulose acetate with the aid ofacetic anhydride, the steps of pretreating .a cellulosic material infibrous form with a medium comprising a mixture of formic acid andacetic acid, said mixture having incorporated therein a small amount ofa mineral acid esterification catalyst, the formic acid being present inan amount of from 1 to 20% by weight of the cellulose, mixing saidpretreated cellulosic material with acetic anhydride under suchconditions that said cellulosic material is partially acetylated whilestill retaining its fibrous form, and then continuing the acetylation bymixing said partially acetylated fibrous cellulosic material with anacetylation mixture comprising acetic anhydride and an esterificationcatalyst.

10. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising a mixture of formic acid andacetic acid, said mixture having incorporated therein a small amount ofsulfuric acid, the formic acid being present in an amount of from 1 to20% by weight of the cellulose, mixing said pretreated cellulosicmaterial with acetic anhydride under such conditions that saidcellulosic material is partially acetylated while still retaining itsfibrous form, and then continuing the acetylation by mixing saidpartially acetylated fibrous cellulosic material with an acetylationmixture comprising acetic anhydride and sulfuric acid.

11. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising a mixture of formic acid andacetic acid, said mixture having incorporated therein a small amount ofsulfuric acid, the formic acid being present in an amount of from 1 to20% by weight of the cellulose, mixing said pretreated cellulosicmaterial with from '77 to of its weight of acetic anhydride whereby saidcellulosic material is partially acetylated while still retaining itsfibrous form, and then continuing the acetylation by mixing saidpartially acetylated fibrous cellulosic material with an acetylationmixture comprising acetic anhydride and sulfuric acid,

12. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps which comprise pretreating a cellulosicma-' terial in fibrous form with a medium comprising a mixture of formicacid and aceticacid, said mixture having incorporated therein a smallamount of sulfuric acid, the formic acid in said pretreatment mixturebeing present in an amount equal to from 1 to 20% on the weight of thecellulosic material, mixing said pretreated cellulosic material withfrom 77 to 130% of its weight of acetic anhydride, whereby saidcellulosic material is partially acetylated while still retaining itsfibrous form, and then continuing the acetylation by mixing saidpartially acetylated fibrous cellulosic material with an acetylationmixture comprising acetic anhydride and sulfuric acid.

13. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising a mixture of formic acid andacetic acid, said mixture having incorporated therein a small amount ofsulfuric acid, the formic acid in said pretreatment mixture beingpresent in an amount equal to from 1 to 20% on the weight of thecellulosic material, mixing said pretreated cellulosic material withfrom 77 to 130% of its weight of acetic anhydride diluted with not morethan an equal amount of acetic acid, whereby said cellulosic material ispartially acetylated while still retaining its fibrous form,-and thencontinuing the acetylation by mixing said partially acetylated fibrouscellulosic material with an acetylation mixture comprising aceticanhydride and sulfuric acid.

I said cellulosic material is partially acetylated while still retainingits fibrous form. and then continuing the acetylation by mixing saidpartially acetylated fibrous cellulosic material with an acetylationmixture comprising acetic anhydride and sulfuric acid.

15. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising a mixture of lower aliphaticacids, said mixture containing, on the weight of the cellulosicmaterial, from 1 to 20% of formic acid, from 20 to 200% of acetic acidandfrom A to 2% of sulfuric acid, maintaining said cellulosic materialat a temperature of from 16 to 50 C. for 30 to 180 minutes, mixing saidpretreated cellulosic material with from 77 to 130% of its weight ofacetic anhydride whereby said cellulosic material is partiallyacetylated while still retaining its fibrous form, and then continuingthe acetylation by mixing said partially acetylated fibrous cellulosicmaterial with an acetylation mixture comprising acetic anhydride andsulfuric acid.

16. In-a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the

steps of pretreating a cellulosic material in fibrous form with a mediumcomprising amixture of.

lower aliphatic acids, said mixture containing. on

the weight of the cellulosic material, from 1 to and then continuing theacetylation by mixing said partially acetylated fibrous cellulosicmaterial with an acetylation mixture comprising ace tic anhydride andsulfuric acid.

17. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising a mixture of formic acid andacetic acid, said mixture having incorporated therein a small amount ofa mineral acid esterification catalyst, the formic acid being present inan amount of from 1 to 20% by weight of the cellulose, mixing saidpretreated cellulosic material with acetic anhydride diluted with notmore than an equal amount of acetic acid under such conditions that saidcellulosic material is partially acetylated while still retaining itsfibrous form, and then continuing the acetylation by mixing saidpartially acetylated fibrous cellulosic material with an acetylationmixture comprising acetic anhydride and an esterification catalyst.

18. In a process for the manufacture of cellulose acetate with the aidof acetic anhydride, the steps of pretreating a cellulosic material infibrous form with a medium comprising amixture of formic acid and aceticacid, said mixture having incorporated therein a small amount ofsulfuric acid, the formic acid being present in an amount of from 1 to20% by weight of the cellulose, mixing said pretreated cellulosicmaterial with acetic anhydride diluted with not more than an equalamount of acetic acid under such conditions that said cellulosicmaterial is partially acetylated while still retaining its fibrous form,and then continuing the acetylation by mixing said partially acetylatedfibrous cellulosic material with an acetylation mixture comprisingacetic anhydride and sulfuric acid.

19. The method for activating cellulose to prepare it foresterification, which comprises treating the cellulose with a mixture ofa fatty acid of 3-4 carbon atoms. #20 part of formic acid based on theweight of the-cellulose, and a small proportion of sulfuric acid untilthe desired activation has occurred.

CLIFFORD I. HANEY. IIERVIN E. MARTIN.

